Apparatus for eliminating compressor stator vibration induced by tip leakage vortex bursting

ABSTRACT

Vibration induced compressor vane failure from tip leakage vortex bursting is eliminated or minimized. By securing the vane at opposite ends to inner and outer stationary casings, tip leakage is entirely avoided hence avoiding the mechanism for inducing vibration. By contouring the inner surface of the flow path to converge the flow in a downstream direction with a cantilevered compressor vane having a vane tip spaced from the inner casing surface, airflow lift off is precluded or minimized maintaining the flow attached to the flowpath surfaces with consequent avoidance of tip vortex induced vibration.

The present invention relates to stator vanes in a compressor betweeninner and outer stationary components and particularly relates toapparatus for minimizing or eliminating tip leakage vortex bursting.

BACKGROUND OF THE INVENTION

In compressors for turbines, stator vanes are typically mounted on afixed or stationary casing surrounding a compressor rotor mountingbuckets. Thus, air flowing into the compressor is compressed and heatedfor flow to various components of the turbine. At the aft end of thecompressor, the stator vanes fixed to the outer stationary component arecantilevered in a radial inward direction and have tips spaced from aninner stationary component. These stator vanes at the aft end of thecompressor are typically used to straighten the flow from thecompressor. As the compressed air flows through the flow path definedbetween the inner and outer stationary components, a portion of thecompressed air flows about the tip of the cantilevered stator vanes fromthe high pressure side to the low pressure side of each of vane, i.e.from the concave side to the convex side. As the flow passes between thetip and the inner stationary component, however, it forms a vortex.Under certain aerodynamic conditions, it has been discovered that thevortex as it bursts from the vane tips can cause a frequency ofvibration in the stator vanes which reinforces the blade naturalfrequency. This can lead to failure of the compressor stator vanes.Accordingly, there is a need for apparatus which will minimize oreliminate tip leakage vortex bursting with consequent induced vibrationsuch that stator vane failure resulting from such induced vibration doesnot occur.

BRIEF DESCRIPTION OF THE INVENTION

In a preferred embodiment of the invention there is provided acompressor comprising: inner and outer stationary casings; and aplurality of stator vanes extending between and secured at radiallyopposite ends to said inner and outer casings thereby eliminating tipleakage between opposite sides of each stator vane and stator vanevibration induced by tip leakage vortex bursting

In a preferred embodiment of the invention, there is also provided acompressor comprising: a stator vane segment including a plurality ofstator blades and inner and outer stationary shrouds about the bladeseliminating tip leakage along the inner shroud and between oppositesides of the inner ends of the stator blades.

In a further preferred embodiment of the invention, there is provided acompressor comprising: a stator vane segment including a plurality ofstator blades and a radial outer shroud, a stationary inner casingspaced from a tip of the stator blades and having a contoured surfaceexposed to the flow path for converging the flow in a downstreamdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary schematic cross-sectional illustration of acompressor and turbine;

FIG. 2 is a fragmentary cross-sectional view of a configuration of acompressor at the aft end of the compressor according to the prior art;

FIG. 3 is a fragmentary cross-sectional view illustrating a stator vanebetween stationary components according to an aspect of the presentinvention;

FIG. 4 is a view similar to FIG. 3 illustrating a further aspect of thepresent invention;

FIG. 5 is a perspective view of a compressor vane segment according toan aspect of the present invention; and

FIG. 6 is a view similar to FIG. 4 illustrating a further aspect of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 there is illustrated a compressor sectiongenerally designated 10 and a turbine section generally designated 12.It will be appreciated that the compressor 10 compresses and heats airfor use by various portions of the turbine 12. Also illustrated is oneof a plurality of combustor cans 14 wherein a portion of the compressedair from compressor section 10 is mixed with fuel and combusted for flowinto the various stages of the turbine 12. The turbine converts thepressurized heated combusted gases into mechanical rotational energywhereby the rotation of the turbine rotor can perform useful work, e.g.,when coupled to a generator to generate electricity. A portion of thatgenerated work is used to rotate the rotor 16 of the compressor 10 toinitially compress the air supplied to the turbine.

As illustrated in FIG. 1, the rotor 16 of the compressor mounts aplurality of buckets 18 for rotation therewith and a plurality of statorvanes 20 fixed to the outer casing 22 of the compressor. At the aft endof the compressor, there are one or more arrays of stator blades 24cantilevered from and fixed to the outer casing 22. In the illustration,there are three axially spaced circumferential arrays ofcircumferentially spaced stator vanes 24. As noted previously, thestator vanes 24 cantilevered between the stationary outer casing 22 andthe stationary inner casing 26 have tips which are closely spaced fromthe inner casing 26 as illustrated in FIG. 2. The gap between the tipsand the inner casing 26 permit flow from the high pressure concave sidesof the stator vanes 24 to the low pressure convex sides of the statorvanes 24 causing the formation of vortices. These vortices have beenfound to have a back and forth frequency component which under certainaerodynamic conditions may reinforce the natural frequency of the statorvanes 24. Should this occur, there is an enhanced possibility that thestator vanes can fail.

To minimize or eliminate this possibility, and referring to FIG. 3,there is illustrated a stator vane 40 comprising one of a plurality ofstator blades or vanes in an annular array of such vanes about the axisof the compressor. The vanes 40 are disposed between the outer fixedstationary casing 42 and an inner fixed cylindrical casing 44. Theopposite ends of the stator vanes are fixed to the casings 42 and 44,respectively. Consequently, the gap between the tip of the stator vaneand the stationary inner casing illustrated in FIG. 2 is closed. Thisprevents the formation of vortices resulting from passage of air betweenopposite sides of each vane about the tip of the vane and hence entirelyeliminates vortex bursting and potential resultant sympatheticvibration.

In another aspect of the present invention as illustrated in FIGS. 4 and5, the vanes 46 extend between a fixed outer casing 48 and a fixed innerpart 50. Each vane 46 may comprise one of a plurality of vanes of acompressor vane segment generally designated 52 in FIG. 5. The segment52 includes an outer shroud or band 54 and an inner shroud or band 56.The vanes 46 extend between the two bands 54 and 56. Each segment 52 maycomprise any number of vanes dependent upon the total blade count in thestage. Consequently, and referring back to FIG. 4, the segment 52 issecured to the outer casing 48 with the vanes and inner band 56cantilevered from the outer casing 48. The radial outer surface of theinner band 56 is preferably contoured. That is, the radially outersurface 58 of the inner band 56 converges in a radial outward anddownstream direction relative to the flowpath of the compressed airdefined between the outer and inner casings.

While it will be appreciated that each stator vane 46 may be fixed toboth the outer and inner bands and hence tip leakage is avoided therebyalso eliminating the excitation source, i.e., the tip leakage vortex, itis also possible to minimize the occurrence of stator vane tip leakagevortex vibration induced vane failure notwithstanding a gap between tipsof cantilevered stator vanes and the opposed inner casing. That is, thestator vanes 46 can remain cantilevered with tips spaced from the innercasing provided the inner casing is contoured to preclude lift off ofthe tip leakage vortex. Thus, if the tip leakage vortex cannot lift offthe contoured surface because of the convergent flow in the downstreamdirection, and remains attached to the inner and outer flow pathdefining surfaces, vibration induced by tip leakage vortex bursting isminimized or eliminated. In FIG. 6, the inner casing 60 has an innerflow surface 62 shaped to converge the flow in a radial outward anddownstream direction. The flow convergence prevents lift off of the tipleakage vortex notwithstanding that the tip of stator blade 64 is spacedfrom casing 60. This minimizes the excitation source which otherwise maypotentially cause stator blade failure.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A compressor comprising: inner and outer stationary casings; and aplurality of stator vanes extending between and secured at radiallyopposite ends to said inner and outer casings thereby eliminating tipleakage between opposite sides of each stator vane and stator vanevibration induced by tip leakage vortex bursting.
 2. A compressorcomprising: a stator vane segment including a plurality of stator bladesand inner and outer stationary shrouds about the blades secured to innerand outer ends of the blades respectively, thereby eliminating tipleakage along the inner shroud and between opposite sides of inner endsof the stator blades.
 3. A compressor according to claim 2 wherein theinner and outer shrouds define a convergent flow path between adjacentstator blades to minimize or eliminate flow lift off from at least oneof said inner and outer surfaces.
 4. A compressor according to claim 3wherein the inner shroud has upstream and downstream surfaces, saiddownstream surfaces extending radially outwardly relative to an axis ofthe compressor a greater distance than upstream surfaces enabling aconvergent flow path.
 5. A compressor comprising: a stator vane segmentincluding a plurality of stator blades and a radial outer shroud, and astationary inner casing spaced from a tip of the stator blades andhaving a contoured surface exposed to the flow path for converging theflow in a downstream direction.